In the field of pneumatic tools, a pneumatic screw punching machine having a construction in which a screw is punched to a certain extent into an objective article by a driver bit coupled to a piston and is then fastened by driving and rotating the driver bit by an air motor.
FIG. 5 of the accompanying drawings shows a cylinder head portion of such a pneumatic screw punching machine. In this drawing, reference numeral 1 denotes a housing and a driver bit 4 is shown coupled to a piston 3 of an air cylinder 2 inside this housing 1. A head cap 5 is coupled by a bolt (not shown) to an open end portion of the housing 1 and a seal 6 is interposed between the housing 1 and the head cap 5 to prevent leak of air of an air chamber 7 inside the housing 1.
A head valve 8 fitted into the head cap 5 is brought into pressure contact with a valve seat 9 of the open edge portion of the air cylinder 2 by a pilot pressure acting on the rear surface (right side in the drawing) under the standby state and cuts off an air passage between the air chamber 7 and the air cylinder 2.
When a stem 12 of a trigger valve 11 is pushed by operating a trigger lever 10 pivotally fitted to the housing 1, the pilot pressure acting on the rear surface of the head valve 8 is discharged and the head valve 8 is moved back by the pressure of the air chamber 7. In consequence, pressure air of the air chamber 7 is supplied into the air cylinder 2, and the piston 3 and the driver bit 4 advance, eject a screw inside a nose (not shown) and punch it into a building material. Subsequently, the air motor (not shown) drives and rotates the driver bit 4 to thereby fasten the screw to the building material.
When any component inside the housing 1 is exchanged or is repaired, the cap fitting bolt is removed to separate the housing 1 and the head cap 5. When the distal end portion of the driver bit 4 is worn out and must be exchanged with new one, for example, the valve seat 9 at the head of the air cylinder 2 is removed or the air cylinder 2 is withdrawn as a whole from the housing 1 to take out the piston 3 and the driver bit 4 and the driver bit 4 is then exchanged.
Therefore, this pneumatic screw punching machine involves the problem that the procedures for disassembly and assembly are much complicated and time-consuming. Another problem is that the head cap 5, the seal 6, the head valve 8 and the valve seat 9 are likely to be assembled in a wrong way or they are likely to be lost, and the seal, etc, are caused to deform during the maintenance operation.
Accordingly, the present invention is directed to solve the problems described above by facilitating maintenance of a pneumatic screw punching machine.